1. Field of the Invention
This invention relates to pinned substrates and more particularly to pinned ceramic substrates.
2. Description of the Prior Art
The use of pinned ceramic substrates for electronic packaging and the like is well known to those skilled in the art, cf. U.S. Pat. Nos. 3,374,110, 3,539,876, 3,540,894, and 3,846,823, for example. Heretofore in the prior art, ceramic substrates have been pinned in a variety of ways.
For example, a prior art system known and referred to herein as a head and bulge system is commonly used to pin ceramic substrates. Essentially, a pin blank is inserted in a larger diameter preformed hole of the substrate such that it protrudes outwardly on each side of the substrate. More particularly, each of the blanks has a small uniform protrusion on one side of the substrate and a longer uniform protrusion on the opposite side of the substrate, the longer protrusions becoming the pluggable parts of the pins formed therefrom. A head is formed on the smaller protrusion of the pin blank on the one side of the substrate and a bulge is formed in the longer protrusion on the other side of the substrate, thereby forming the pin. As such, the substrate surrounding the hole and lying under the head and under the bulge becomes tightly wedged therebetween thus affixing or securing the pin to the substrate per se or in combination with the type of mechanical press fit, e.g., snug fit, frictional fit, tight fit, medium-force fit, or heavy-force fit, effected between the pin and substrate hole wall. Examples of such prior art systems are described in U.S. Pat. Nos. 3,216,097; 3,257,708; and 3,768,134.
However, because of the somewhat brittle nature of the ceramic, these prior art systems are not entirely satisfactory. More specifically, because the pin remains in its solid or plastic state during the head and bulge forming operations, the ceramic is often chipped, crushed, cracked and/or otherwise damaged by the pins during these operations. While, prior art systems such as, for example, the ones described in U.S. Pat. No. 3,735,466 and the publication entitled "Low-Stress Pin Insertion", R. J. Modlo et al, IBM Technical Disclosure Bulletin, Vol. 22, No. 8B, January 1980, pages 3649-3650, mitigate to some extent the damage to the ceramic substrates, caused by such operations they too are not entirely satisfactory because the pins still remain in a solid or plastic state during these operations and can thus cause damage to the ceramic substrate.
In certain prior art systems of the pinned ceramic substrate types, a headless pin is press fit into the hole of the substrate and an end of the pin is solder bonded to a conductive line carried on the appropriate metallized surface of the ceramic surface. A bulge may or may not be formed in the pin. The devices of U.S. Pat. Nos. 4,082,394 and 4,092,697 are examples of each of these prior art systems. However, because the pin remains in its solid or plastic state as it is being press fit into the substrate hole and/or during the bulge forming operation, it can still effect damage to the ceramic substrate.
Another prior art system is described in U.S. Pat. No. 3,736,651. In this system, the pins are provided with heads and are inverted such that the tops of the heads are solder bonded to metallic contact pads carried on an appropriate metallized surface of the ceramic substrate. As such, the pins are not located within any hole in the substrate, but are completely externally mounted to the substrate. The interconnection is thus merely limited to the solder bond between the pin head and the pad and hence is not as reliable or as mechanically stable as in the system where the pin is located in a substrate hole.
Another prior art pinned ceramic substrate system is described in the publication entitled "Pinning Technique for Ceramic Module", J. R. Lynch, IBM Technical Disclosure Bulletin, Vol. 14, No. 1, June 1971, pages 174-175. It uses a shrink-fit like principle to affix the pins thereof in the holes of a ceramic substrate. To do this, the ceramic substrate must be provided in pressed unfired, i.e. uncured, form with preformed holes. Copper pin blanks of smaller diameter are inserted into the substrate holes. The blanks extend on through the substrate holes and into correspondingly aligned holes of a graphite mold and locating fixture which supports the blank-loaded substrate and is used to cast the pins as a result of the blanks being melted in the subsequent firing cycle of the ceramic substrate.
The assembly when it is run through the ceramic firing cycle melts the copper blanks as aforementioned and cures the ceramic. After the copper solidifies, the firing shrinkage associated with the ceramic substrate causes the ceramic to shrink around the copper resulting in a pinned part which has the cast pin locked into the ceramic, but not into the graphite mold because of the different coefficients of expansion of the copper and graphite. Again, in this system because the copper is required to return to its solid or plastic state before the ceramic can effectively shrink around it, the ceramic substrate is subject to damage as it contracts around the copper. Moreover, the associated process requires precise control for processing. Because of its fabrication complexity, the aforedescribed pinned ceramic substrates are not conducive to being fabricated in a simple and reliable manner and on a mass production basis.
Moreover, the high temperatures required to cure the ceramic and melt the copper, necessitates the use of a graphite mold in the last-mentioned prior art system and hence necessitates the use of a non-consumable mold. In addition, because the ceramic undergoes substantial shrinkage as a result of being cured, whereas the mold is substantially uneffected shrinkage-wise, the recast pins were subject to being deformed because of the mismatch in the shrinkage properties of the ceramic and graphite mold.
Other prior art systems for pinning ceramic substrates using preformed pin blanks are described, for example, in U.S. Pat. No. 3,518,756.
One way to overcome the problems associated with the aforedescribed prior art systems is described in the aforementioned co-pending patent application, Ser. No. 223,190, filed Jan. 7, 1981, entitled "Pinned Substrate Apparatus", D. E. Houser, the other aforementioned co-pending application Ser. No. 223,191 describing a machine that can be used to make the pinned substrate apparatus of the aforementioned application, Ser. No. 223,190. Briefly, a pin blank is inserted into a preformed hole of a ceramic substrate. The blank is impacted with a force that temporarily places the blank in a viscoelastic fluid state. While in this temporary state, some of the pin blank part, which is in the hole, flows between the ceramic particles surrounding the hole. When the pin blank returns to it undisturbed solid state, a solid extension, which is integral with the core or main body of the pin blank, is formed from the aforedescribed pin blank flow effected between the ceramic particles and is in interlocking engaged relationship with the ceramic particles.
The present invention is another way for overcoming the aforementioned problems, as will become apparent hereinafter.
It is to be understood that it is known in the prior art to sinter dry metallic particles in previously filled via or transverse holes of a ceramic substrate and to subsequently apply preformed non-powdered metallurgy pins to the resultant formed sintered members in the vias or holes., cf. U.S. Pat. No. 3,561,110, assigned to the common assignee herein. Also it is known to use consumable molds or fixtures in the fabrication of certain electrical components. For example, the use of a meltable, vaporizable or otherwise oxidizable tube or casing containing material for making an incandescent filament is described in U.S. Pat. Nos. 349,572, 930,723, 936,403, and 1,701,342. The use of consumable molds in other electrical and in non-electrical arts is described, for example, in U.S. Pat. Nos. 786,257 and 2,412,925, and in U.S. Pat. Nos. 2,464,437, 3,049,795, and 3,201,858, respectively.
However, none of the prior art of which we are aware contemplates providing a pinned ceramic substrate in accordance with the principles of the present invention.